4 ms·

Let me guess: you implicitly assume that cost is proportional to volume, because that is roughly true for a fission reactor, which is filled with fuel and contr

by T-A 7y ago

Let me guess: you implicitly assume that cost is proportional to volume, because that is roughly true for a fission reactor, which is filled with fuel and control rods. But in a tokamak reactor, you have a large container with all the expensive engineered stuff placed around its surface, so cost should be roughly proportional to surface area, or volume^(2/3).

pfdietz 7y ago
Fusion reactors are MUCH more complex than fission reactors. So, just comparing volume is being very favorable to fusion. There should be a complexity multiplier in there as well, but that's difficult to quantify. This complexity also means keeping that fusion reactor running would be a nightmare. Complex things break, and the fusion reactor will be so irradiated that hands on maintenance will be impossible. I will add that fission power plants are uncompetitive even if you ignore the cost of the reactor itself.
- T-A 7y ago
  > Fusion reactors are MUCH more complex than fission reactors. So, just comparing volume is being very favorable to fusion. That's a non sequitur. Your volume comparison can, at best, tell you how cost scales with reactor power. If the exponent is wrong, it serves no valid purpose at all.
  - pfdietz 7y ago
    Complex things being more expensive than simple things is a non sequitur? Surely your apparent position, that something made of superconductors is going to be just as cheap as something made of steel, is much more supportable! /s And I wasn't talking about an exponent there.
    - T-A 7y ago
      > Complex things being more expensive than simple things is a non sequitur? No. The statement "Fusion reactors are MUCH more complex than fission reactors." followed by "So, just comparing volume is being very favorable to fusion." is a non sequitur. > And I wasn't talking about an exponent there. Your compared power/volume ratio, implying that cost is proportional to volume (otherwise, the comparison is pointless). I pointed out that the different operating principles of fission and fusion reactors suggest cost proportional to volume^(2/3) for the latter (which of course implies that there is a size beyond which a fusion reactor will be more cost efficient than a fission one). The 2/3 is known as an exponent. I believe exponents are part of the K-12 math curriculum, and definitely propaedeutic to nuclear engineering.
      - pfdietz 7y ago
        > No. The statement "Fusion reactors are MUCH more complex than fission reactors." followed by "So, just comparing volume is being very favorable to fusion." is a non sequitur. You seem to be implying that comparing by volume is unfair to fusion. So, instead, let's compare by mass. The mass of ITER is 23,000 tonnes, for an average density of about 2.8 g/cm^3. I don't have the figure for the mass of a PWR reactor vessel in front of me, but it's mostly empty space (filled with water and fuel in operation, which are not part of the capital cost). So, comparing by volume alone may actually ALSO be giving fusion an advantage. > I pointed out that the different operating principles of fission and fusion reactors suggest cost proportional to volume^(2/3) for the latter (which of course implies that there is a size beyond which a fusion reactor will be more cost efficient than a fission one). I don't think scaling data for cost of fusion experiments supports this. BTW, as a fusion reactor gets bigger, at a fixed geometry and magnetic field strength, the mass of the material needed to support the magnets (to resist the outward force the magnetic field puts on the coils) is proportional to the volume of the reactor, not to the surface area of the plasma. And you want the reactor to be at as high magnetic field as possible, since the fusion power density goes as B^4. If wall power loading prevents one from taking advantage of this the reactor is too big and will have inferior power density, compared to a smaller reactor at higher B. This is why concepts like MIT's ARC have power density an order of magnitude higher than ITER (but still very much less than a PWR). > The 2/3 is known as an exponent. I believe exponents are part of the K-12 math curriculum, and definitely propaedeutic to nuclear engineering. That's very special, I'm sure.
        T-A 7y ago
        > You seem to be implying that comparing by volume is unfair to fusion I am pointing out an obvious logical fallacy. If it really isn't obvious, try substituting "Tesla cars" for "fusion" and "bars of gold" for "fission reactors". Here's what you get: "Tesla cars are MUCH more complex than bars of gold. So, just comparing volume is being very favorable to Tesla cars." Which of course is utter nonsense. A Tesla Model 3 occupies roughly 10 m^3 (order of magnitude, mind you); that volume of gold would weigh about 19.3e4 kg, which at the current price of $45.6e3/kg would be worth about $8.8 billion. Clearly, the MUCH more complex Tesla Model 3 costs quite a bit less than the same volume in gold. > So, instead, let's compare by mass. That would be equally pointless. Instead, how about taking a moment to look up a serious economic analysis? Here is a fairly recent one, open access and all: https://www.sciencedirect.com/science/article/pii/S0360544218305395 https://www.sciencedirect.com/science/article/pii/S036054421... It compares existing power plants with four tokamak conceptual designs which "span a range from relatively near-term concepts, based on limited technology and plasma physics extrapolations, to a more advanced conception". Upon reading it, you will be happy to learn that it finds Total Cost Of Electricity (TCOE) produced by those fusion reactors to be slightly higher than the lowest cost alternative, fission reactors. All other options considered (combined-cycle gas turbines, open-cycle gas turbines, coal plants, solar large photovoltaic plants, onshore and offshore wind plants) turn out to be more expensive.

by T-A 7y ago

pfdietz 7y ago

Fusion reactors are MUCH more complex than fission reactors. So, just comparing volume is being very favorable to fusion. There should be a complexity multiplier in there as well, but that's difficult to quantify. This complexity also means keeping that fusion reactor running would be a nightmare. Complex things break, and the fusion reactor will be so irradiated that hands on maintenance will be impossible. I will add that fission power plants are uncompetitive even if you ignore the cost of the reactor itself.

T-A 7y ago
> Fusion reactors are MUCH more complex than fission reactors. So, just comparing volume is being very favorable to fusion. That's a non sequitur. Your volume comparison can, at best, tell you how cost scales with reactor power. If the exponent is wrong, it serves no valid purpose at all.
- pfdietz 7y ago
  Complex things being more expensive than simple things is a non sequitur? Surely your apparent position, that something made of superconductors is going to be just as cheap as something made of steel, is much more supportable! /s And I wasn't talking about an exponent there.
  - T-A 7y ago
    > Complex things being more expensive than simple things is a non sequitur? No. The statement "Fusion reactors are MUCH more complex than fission reactors." followed by "So, just comparing volume is being very favorable to fusion." is a non sequitur. > And I wasn't talking about an exponent there. Your compared power/volume ratio, implying that cost is proportional to volume (otherwise, the comparison is pointless). I pointed out that the different operating principles of fission and fusion reactors suggest cost proportional to volume^(2/3) for the latter (which of course implies that there is a size beyond which a fusion reactor will be more cost efficient than a fission one). The 2/3 is known as an exponent. I believe exponents are part of the K-12 math curriculum, and definitely propaedeutic to nuclear engineering.
    - pfdietz 7y ago
      > No. The statement "Fusion reactors are MUCH more complex than fission reactors." followed by "So, just comparing volume is being very favorable to fusion." is a non sequitur. You seem to be implying that comparing by volume is unfair to fusion. So, instead, let's compare by mass. The mass of ITER is 23,000 tonnes, for an average density of about 2.8 g/cm^3. I don't have the figure for the mass of a PWR reactor vessel in front of me, but it's mostly empty space (filled with water and fuel in operation, which are not part of the capital cost). So, comparing by volume alone may actually ALSO be giving fusion an advantage. > I pointed out that the different operating principles of fission and fusion reactors suggest cost proportional to volume^(2/3) for the latter (which of course implies that there is a size beyond which a fusion reactor will be more cost efficient than a fission one). I don't think scaling data for cost of fusion experiments supports this. BTW, as a fusion reactor gets bigger, at a fixed geometry and magnetic field strength, the mass of the material needed to support the magnets (to resist the outward force the magnetic field puts on the coils) is proportional to the volume of the reactor, not to the surface area of the plasma. And you want the reactor to be at as high magnetic field as possible, since the fusion power density goes as B^4. If wall power loading prevents one from taking advantage of this the reactor is too big and will have inferior power density, compared to a smaller reactor at higher B. This is why concepts like MIT's ARC have power density an order of magnitude higher than ITER (but still very much less than a PWR). > The 2/3 is known as an exponent. I believe exponents are part of the K-12 math curriculum, and definitely propaedeutic to nuclear engineering. That's very special, I'm sure.
      - T-A 7y ago
        > You seem to be implying that comparing by volume is unfair to fusion I am pointing out an obvious logical fallacy. If it really isn't obvious, try substituting "Tesla cars" for "fusion" and "bars of gold" for "fission reactors". Here's what you get: "Tesla cars are MUCH more complex than bars of gold. So, just comparing volume is being very favorable to Tesla cars." Which of course is utter nonsense. A Tesla Model 3 occupies roughly 10 m^3 (order of magnitude, mind you); that volume of gold would weigh about 19.3e4 kg, which at the current price of $45.6e3/kg would be worth about $8.8 billion. Clearly, the MUCH more complex Tesla Model 3 costs quite a bit less than the same volume in gold. > So, instead, let's compare by mass. That would be equally pointless. Instead, how about taking a moment to look up a serious economic analysis? Here is a fairly recent one, open access and all: https://www.sciencedirect.com/science/article/pii/S0360544218305395 https://www.sciencedirect.com/science/article/pii/S036054421... It compares existing power plants with four tokamak conceptual designs which "span a range from relatively near-term concepts, based on limited technology and plasma physics extrapolations, to a more advanced conception". Upon reading it, you will be happy to learn that it finds Total Cost Of Electricity (TCOE) produced by those fusion reactors to be slightly higher than the lowest cost alternative, fission reactors. All other options considered (combined-cycle gas turbines, open-cycle gas turbines, coal plants, solar large photovoltaic plants, onshore and offshore wind plants) turn out to be more expensive.